1. Field of the Invention
The present invention relates generally to capacitor-based high energy pulse forming networks.
2. Discussion of the Related Art
In certain applications where high power sources (e.g., power lines, batteries) are unable to deliver high levels of peak power, pulse forming networks having high-energy density capacitors are often used. In these applications, the capacitors are slowly charged from the power source and then quickly discharged for short time periods to provide pulsed energy at high peak power levels. The capacitors are typically used with large inductors to restrict the flow of energy from the capacitors and to establish the frequency, period and shape of the output pulse from the network.
FIG. 1 illustrates a known pulse forming network 100 including a number n of modules 102n (where n=1, 2, . . . , N) coupled to a load 104. Each module 102n includes a bank of capacitors 106n coupled to the load 104 through an inductor 110n via a switch 108n and an anti-reversing diode 112n. In operation, each bank of capacitors 106n is charged while the switches 108n are open. Once charged, groups of modules 102n are sequentially discharged to the load 104. For example, initially, a predetermined number of modules (a first set of modules) are discharged at once to the load 104. That is, the switches 108 for the first set of modules are closed at once, discharging the energy stored through the inductors 110 corresponding to the first set of modules to the load producing a current pulse to the load 104. At a point in time after the discharge of the first set of modules is initiated, a second set of modules 102 are discharged at once to the load producing a second current pulse to the load. After the initiation of the discharge of the second set of modules, a third set of modules is discharged at once to the load producing a third current pulse, and so on. The pulses add, creating the output pulse waveform at the load. The anti-reversing diodes 112n of each module 102n prevent the voltage from reversing on the capacitors (which prevents the capacitors from recharging from their own discharge current) and ensure that the current discharging from other sets of modules flows to the load 104. Typically, in most high power pulse forming networks, there are 3-5 sets of modules, each set being discharged at the same time, the sets being discharged in sequence.
FIG. 2 is a graph of current over time illustrating a typical pulse waveform formed by the pulse forming network 100 of FIG. 1 including 72 modules (i.e., N=72) divided into 3 sets of modules. For example, modules 1021-10224 are then discharged at the same time forming current pulse 202, modules 10225-10248 are then discharged at the same time forming pulse 204, and modules 10249-10272 are discharged at the same time forming pulse 206. The pulses add to produce waveform 208 as compared to the desired flat top waveform 201, emulating a square or rectangular pulse.
This pulse forming network results in many inductors (e.g., 72 in this example) representing a large mass in the pulse forming network. Furthermore, the waveform 208 does not accurately track the desired flat top waveform 201, especially at the end of the waveform. Additionally, significant energy is wasted at the end of the waveform (which is illustrated as area 212 under the curve of waveform 208). Accordingly, the energy storage requirements of the pulse forming network 100 must be increased in order to provide enough current in view of the wasted energy. Requiring many large inductors and needing to provide additional energy storage due to wasted energy adds to the mass and size of the pulse forming network, as well as increases the flux generated by the inductors.